Process of making sulfate of aluminium.



" v UNIT D, TA

Patented m 1115, 1904.

HOWARD SPENCE, or MANCHESTER, E rem-m "PROCESS oF-mAKme SULFATE Q ALUMIN U 1 u SPECIFICATION forming part of Letters lPatent No; 754,824, dated March 15, 1904.

Application filed April 20,19J3-- Serial No. 153,374. (E0 specimens.)

To all whom it may concern:

Be it known that I, HOWARD SPEXOE, a subject of the King of Great Britain and Ireland, residing at Manchester, in the county of Lancaster, England, have invented new and useful Improvements in the Proces of Making Aluminium Sulfate, of which thefollowingi a specification.

An important desideratum for rarious in dustrial purposesis a sulfate of alumina which shall contain materially less sulfuric acid than that required by the formula A1203. 3803.

By my present invention Iam enabled not only to produce a soluble crystallized sulfate of alumina which contains only two molecules of S03 for each molecule of A1203, but also to effect at the same time a very high degree of purification, thus allowing of the employment of low-grade materials for the manufacture'of;

high-grade product. f

In-the specification of the French Brevet dlnvention No. 132,204, dated August 12, 1879,3farguerite claims the manufacture of sulfateloflalumina having the formula Atoasos by the following process: Ammonia alum 1s carefully heated in retorts to drive off the water, the sulfate of ammonia, and a little of the sulfuric acid. The calcined residue is treated with a little water, whereby heat is evolved. The resulting pasty mass sub mitted to a slow evaporation at the ordinary temperature is in part spontaneously and little by little changed to the crystallized basic sulfate, which is separated from the remaining pasty sulfates .by washing with cold water. Partial desulfatization is also claimed of ordinary or neutral sulfate of alumina either by heat alone or assisted by the presence of chemical agentsfsuch as lime, baryta, alumina, oxid of zinc, iron, or their carbonates or other compounds-either by these agents in the cold or by all other means capable of yielding the product which he proposed to patent. No working directions or data are given for the preparation of basic sulfate except in the case of the process/fordecornposing ammonia alum by heat.

The following later description by Mar- LPATENIT' O FIC tion of the acid by engaging'it in other com- .binations; second, by eliminatinga certain quantity and adding alumina. By the first the method'of reduction which succeeds best 1s the treatment with zinc; but in this way only small quantities of the sesquibasic sulfate are obtained. The second method re quires excessire additions, but with care it admits of obtaining the sulfate in question.

Pickering (Chemical News 45, page 133, A. D. 1882 contro'verts Marguerites statement as to the existence" of the basic sulfate of alumina. This indicates that the compound had not then {as it has not sincelbeen com mcrcially produced.

-It is well known that alumina as existing in. its commonly-available sources, such as bauxite and co'mme'rcial-i. a, crystalline hydrate of alomina-is not soluble under ordinary circumstances or conditions to any con side'rable extent in solutions of neutral or basic sulfate of alumina without excessive iom both of Also: and S03 in an insoluble form. For this reasouthe sulfates of alumina of commerce rarely contain more than about three or four per cent. of their total alumina in the basic conditionthat is to say, in execs of the alumina theoretically required to combine as neutral sulfate with the available sulfuric acid present-unless such basicity has been produced by the addition of soda, magnesi or other soluble base. I

V The gelatinous form of hydrhte of alumina sulfate of alumina, is not, on account of its high cost of production, available as a commercial source of alumina, and therefore need not be taken into consideration.

Now we have found that if alumina in or dinary sources besubjected-in excessproportion over that theoretically required to form neutral sulfate to the action of hot sulfuric 9o prepared from soluble salts of alumina by the; action of alkali, although soluble in neutral acid under pressure. as is describet in the;v

b obtain do not, however, allow of an advantageous pt'OfillCtiOD of the crystallized basic sulfate in respect of the'perce'ntage yield ob-. tained therefrom. If, however, it is desired for any special reason to. obtain a small percentage only of the total alumina in the form 7 of the crystallized basic sulfate-as, for example, in cases where it may be necessary to remove in the mother-liquor a large amount of soluble impuritythese solutions (freed from any insoluble matter they contain)-may,

2 5 as hereinafter described, becrystallizcd to effeet the separation therefrom of the erystailized basic sulfate. Thus a basicity as low as thirteen percent. is equal to a ratio of basic 5 to oidinar sulfate of about and consequently a. proportionally low-percentage yield of theformer on the total amount of alumina employed would result.

Separation of the basic and ordinary sulfate 1 by crystallization is not very readily effected when the basicity is lower than the above ratio.

F or the most economical and practical production of the basic sulfate it is desirable to 40 havea basicity of about twenty-two to twentyeight per cent.

\Ve have found that by the addition to the above-named solutions-that is, those solutions which have been rendered as highly 1 basic as practicable consistent with the eco nomical utilization of materialof a sutiieiency of finely-divided lime, most advantageously in the form of carbonate, the desired basieity is readily and practically obtained.

A still higher percentage of basicity is readi ilyobtained, if desired.

1 The carbonate of lime.ad\'antageously in the form of a cream, is best added to the warm or hotsolution of partially-basic sulfate of f 5f alumina having aspecific gravity of about 1.35 to 1.4.0. with agitation during the addition.

The resulting solution .can then be readily separated'froni the suspended insoluble matter by'nieans of a filter-press or otherwise. Since a considerable proportion of the neces- Z sary basieity is obtained by-the previous solution of an excess proportion of Al-iOa a very 1 much smaller addition of carbonate of lime is necessary than would otherwise be the case. 5 and the amount of precipitatedealeium suli Zsulfate of alumina.

fate is consequently less. If the'whole of the desired basicity were to be produced by the addition of lime, the quantity of insoluble matter would be highly disadvantageous.

We have found that a ,hot and strong solution of basic sulfate of alumina in prolonged contact with precipitated calcium sulfate shows a tendencyto decompose and precipi tate alumina in an insoluble form. CQDSG.

quent-lythe basic liquor should i be separated i as rapidly as practicable from the suspended insoluble matter. l

The elearsolu on is now concentrated, most advantageousl' in vacuum yessel's, to a spe: cilic gravity. about 1.45 when tested at 0 about it) Centigrade and thereafter cooled to effect the separation of the crystallized basic Basie sulfate crystallizcs out readily from the liquor, the neutral sulfate remaining in solution as mother-liquor. 8 5

The first formation of the crystals is assisted by the addition during cooling'ot' a small amount of crystals from a prev-ions operation.

The unaltered neutral sulfate of alumina present hasa marked precipitating effect onv 6' the basic sulfate, and for thisreason, as welt as for thepurpose of supplyinga medium for the removal of impurities, it is advisable not tobringthepereentageof-t-hehasiealuminatoo' v 5 near to the theoretical thirty-three per cent. i Agitation of the liquid-duringcoolingalsoacts beneficially in accelerating the formation of the crystals. When the brei formed is sufficiently cooled, the crystals are separated by known means from the mother --liquor. 10 The mother-liquor containing ordinary sulfate of alumina, together with some basic sulfate of alumina, 'may be treated by known means for the recovery and utilization of the valuable ingredients it contains. to If the sulfate of alumina employed contains any considerable proportion of ferric sulfate, it is advantageous to reduce it to ferrous sulfate, as thereby the quality of the basic sulfate is improved. This reduction may con- 11 vcniently be effected by the addition. to the liquor previous to filtration of a small proportion of calcium sullid in the form of alkali waste, which, moreover, aids in rendering the solution basic and also assists in the 1 1 j purification of the product by its precipitation of sulhd of arsenic if arscmcal sulfuric i acid has been employed.

The crystallized basic sulfate ofalumina produced as hereinbefore described is in a highly-suitable form for employment in vari- ;ous' industries and for the preparation of other compounds of alumina. It is easily j soluble in water and may be readily dried, so

as to obtain it with a very high percentage of I alumina.

The following is a practical example of the process, giving the required details of time,

; temperature, &e.-'- 5 Example: t1 (forty-one) lmndredweights I 25 maintained at about 80 to 90 of bauxite containing sixty-five per cent. AhOs were rapidly mixed with 111% hundredweights (one hundred and eleven and threequarter hundredweights) of sulfuric acid ate specific gravity of 1.475 at 35 centigrade and the mixture run into a lead-lined autoclave. team was then blownin until the pressure rose to twenty pounds per square inch, after which the heat of combination was sufficient to complete the reaction, and-steam wasshut off. The pressure rose rapidly,

. reaching a maximum of seventy-eight pounds per square inch about ten minutes after the steaniwas shut off. From this maximum the pressure fell gradually to, within about two hours, forty pounds per square inch; The which has a basicity of 10.2 per cent,

outof the autoclave into a charge, was then blown lead-linecl tank, was diluted to a specific grav- 2'0 ity of about 1.39 at 90 centigrade, and was treated with 12?; hundredweights (twelve and a quarter hundredweights) of finely-divided -calcium carbonate mixed with water to a creamy consistency, the temperature being.

centigrade, and the mixture agitated. The insoluble matter was then separated and washed in a filterpress. The filtrate of 26.5 per cent. basicity and 1.315 specific gravity at centigrade 3 was then evaporated under vacuum to a specific gravity of 1.4-5 at 7 0 centigrade and was subsequently cooled with agitation. At atemperature of 22 centigrade about 80 per cent. of the basic s'ulfate of alumina present 35 crystallized out,v the breiof crystals and motherliquor being subsequently separated in a centrifugal machine. 7

Having described my invention, what I desire to claim is- 4 1. The process for the manufacture of crystallized sulfate of alumina containing two molecules of S03 for each molecule of AlzO;

which consists in subjecting alumina in excess to the action of hot sulfuric acid under pressure I so as to obtain a solution of sulfate of alumina. containing an excess of alumina, treating this solution with available lime suspended in water until the desired basicity is obtained, filtering the resulting mixture, evaporating the filtered solutionand separating the crystallized basic sulfateitherefrom, substantially as described. l

2. In the manufactureof crystallized basic sulfate of alumina, in subjecting alumina in excess to the action of hot sulfuric acid under pressure so as to obtain,v a solution ofsulfate of alumina containing' an excess of alumina, substantially as described. i

3.v In the manufacture of'crystallized basic sulfate of alumina, the process whichconsists in treating a solution of sulfate of alumina containing an excess of alumina with available lime suspended in water until the desired basicity is obtained, filtering the resulting mixture, evaporating th-e'filtered solutionthe process which consists and separating the crystallized basic sulfate therefrom, substantially as described.

4. In the manufacture of crystallized basic sulfate of alumina, the process which consists in treating a solution of sulfate'of alumina containing an excess of alumina, with available lime suspended in water until the desired basicity is obtained and filtering 01f the resuiting solution from the insoluble matters, substantially as described. In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

' HOWARD SPENGE.

Witnesses: i NVI LIAM GEO. HEYS, ERNALD SnuPsoN Mosnmir; 

